A Stimulator ASIC Featuring Versatile Management for Vestibular Prostheses

A High Precision, Wide Dynamic Range Closed-Loop Neuromodulation IC With Rapid Stimulation Artifact Recovery

This article presents a high precision, wide dynamic range (DR) closed-loop neuromodulation (CLNM) system that can completely reject stimulation artifacts (SA) and achieve rapid SA recovery. In the recorder, a novel SA quick-blanking scheme is proposed for rail-to-rail SA rejection while minimizing SA recovery time. Besides, a new analog front-end (AFE) architecture based on a frequency-shaping (FS) technique is developed to extend DR intrinsically. In the stimulator, a stimulation driver implemented with a proposed redundant crossfire (RXF) technique is incorporated to improve the effective resolution of the stimulation current. The designed CLNM system is implemented in a 180 nm Bipolar-CMOS-DMOS (BCD) process. Measurement results show that the system is capable of tolerating rail-to-rail (5 V) SA and reducing the SA recovery time from 12 ms to 0.15 ms. The FS recorder extends the DR at low frequencies (LF) to 17.5 bits to enhance tolerance to LF interferences. The proposed stimulator adopting the 4-way RXF topology improves the effective resolution to 12.75 bits without consuming much extra area and power. Animal experiments demonstrate that the designed system can acquire high-fidelity neural signals immediately after stimulation onsets, thus supporting concurrent recording and stimulation.

A Multi-Channel Stimulator With High-Resolution Time-to-Current Conversion for Vagal-Cardiac Neuromodulation

This paper presents a low power integrated multi-channel stimulator for a cardiac neuroprosthesis designed to restore the parasympathetic control after heart transplantation. The proposed stimulator is based on time-to-current conversion. It replaces the conventional current mode digital-to-analog converter (DAC) that uses tens of microamps for biasing, with a novel capacitor time-based DAC (CT-DAC) offering about 10-bit current amplitude resolution with a bias current of only 250 nA. A stimulator chip was designed in a 0.18 μm CMOS high-voltage (HV) technology. It consists of 16 independent channels, each capable of delivering up to 550 μA stimulus current with a HV output stage that can be operated up to 20 V. The stimulator chip performance was evaluated using both RC equivalent load and a microelectrode array in saline solution. It is power efficient, provides high-resolution current amplitude stimulation, and has good charge balance. The design is suitable for multi-channel neural stimulation applications.

A Versatile Hermetically Sealed Microelectronic Implant for Peripheral Nerve Stimulation Applications

This article presents a versatile neurostimulation platform featuring a fully implantable multi-channel neural stimulator for chronic experimental studies with freely moving large animal models involving peripheral nerves. The implant is hermetically sealed in a ceramic enclosure and encapsulated in medical grade silicone rubber, and then underwent active tests at accelerated aging conditions at 100°C for 15 consecutive days. The stimulator microelectronics are implemented in a 0.6-μm CMOS technology, with a crosstalk reduction scheme to minimize cross-channel interference, and high-speed power and data telemetry for battery-less operation. A wearable transmitter equipped with a Bluetooth Low Energy radio link, and a custom graphical user interface provide real-time, remotely controlled stimulation. Three parallel stimulators provide independent stimulation on three channels, where each stimulator supports six stimulating sites and two return sites through multiplexing, hence the implant can facilitate stimulation at up to 36 different electrode pairs. The design of the electronics, method of hermetic packaging and electrical performance as well as in vitro testing with electrodes in saline are presented.

Quantification of clinically applicable stimulation parameters for precision near-organ neuromodulation of human splenic nerves

Neuromodulation is a new therapeutic pathway to treat inflammatory conditions by modulating the electrical signalling pattern of the autonomic connections to the spleen. However, targeting this sub-division of the nervous system presents specific challenges in translating nerve stimulation parameters. Firstly, autonomic nerves are typically embedded non-uniformly among visceral and connective tissues with complex interfacing requirements. Secondly, these nerves contain axons with populations of varying phenotypes leading to complexities for axon engagement and activation. Thirdly, clinical translational of methodologies attained using preclinical animal models are limited due to heterogeneity of the intra- and inter-species comparative anatomy and physiology. Here we demonstrate how this can be accomplished by the use of in silico modelling of target anatomy, and validation of these estimations through ex vivo human tissue electrophysiology studies. Neuroelectrical models are developed to address the challenges in translation of parameters, which provides strong input criteria for device design and dose selection prior to a first-in-human trial.

Due to the difference between rodent, porcine and human nerve morphology, Gupta et al. propose an integrative approach of computational modelling and ex vivo electrophysiology studies to identify clinically relevant optimal parameters for human peripheral nerve stimulation as a therapeutic tool. The agreement between results validate the use of computer simulations as a first step toward determining stimulation parameters to provide input criteria for device design and dose selection prior to first-in-human trials.

An ASIC for Recording and Stimulation in Stacked Microchannel Neural Interfaces

This paper presents an active microchannel neural interface (MNI) using seven stacked application specific integrated circuits (ASICs). The approach provides a solution to the present problem of interconnect density in three-dimensional (3-D) MNIs. The 4 mm² ASIC is implemented in 0.35 μm high-voltage CMOS technology. Each ASIC is the base for seven microchannels each with three electrodes in a pseudo-tripolar arrangement. Multiplexing allows stimulating or recording from any one of 49 channels, across seven ASICs. Connections to the ASICs are made with a five-line parallel bus. Current controlled biphasic stimulation from 5 to 500 μA has been demonstrated with switching between channels and ASICs. The high-voltage technology gives a compliance of 40 V for stimulation, appropriate for the high impedances within microchannels. High frequency biphasic stimulation, up to 40 kHz is achieved, suitable for reversible high frequency nerve blockades. Recording has been demonstrated with mV level signals; common-mode inputs are differentially distorted and limit the CMRR to 40 dB. The ASIC has been used in vitro in conjunction with an oversize (2 mm diameter) microchannel in phosphate buffered saline, demonstrating attenuation of interference from outside the microchannel and tripolar recording of signals from within the microchannel. By using five-lines for 49 active microchannels the device overcomes limitations when connecting many electrodes in a 3-D miniaturized nerve interface.

A Multichannel High-Frequency Power-Isolated Neural Stimulator With Crosstalk Reduction

In neuroprostheses applications requiring simultaneous stimulations on a multielectrode array, electric crosstalk, the spatial interaction between electric fields from various electrodes is a major limitation to the performance of multichannel stimulation. This paper presents a multichannel stimulator design that combines high-frequency current stimulation (using biphasic charge-balanced chopped pulse profile) with a switched-capacitor power isolation method. The approach minimizes crosstalk and is particularly suitable for fully integrated realization. A stimulator fabricated in a 0.6 μm CMOS high-voltage technology is presented. It is used to implement a multichannel, high-frequency, power-isolated stimulator. Crosstalk reduction is demonstrated with electrodes in physiological media while the efficacy of the high-frequency stimulator chip is proven in vivo. The stimulator provides fully independent operation on multiple channels and full flexibility in the design of neural modulation protocols.

16-Channel biphasic current-mode programmable charge balanced neural stimulation

BACKGROUND

Neural stimulation is an important method used to activate or inhibit action potentials of the neuronal anatomical targets found in the brain, central nerve and peripheral nerve. The neural stimulator system produces biphasic pulses that deliver balanced charge into tissue from single or multichannel electrodes. The timing and amplitude of these biphasic pulses are precisely controlled by the neural stimulator software or imbedded algorithms. Amplitude mismatch between the anodic current and cathodic current of the biphasic pulse will cause permanently damage for the neural tissues. The main goal of our circuit and layout design is to implement a 16-channel biphasic current mode programmable neural stimulator with calibration to minimize the current mismatch caused by inherent complementary metal oxide semiconductor (CMOS) manufacturing processes.

METHODS

This paper presents a 16-channel constant current mode neural stimulator chip. Each channel consists of a 7-bit controllable current DAC used as sink and source current driver. To reduce the LSB quantization error and the current mismatch, an automatic calibration circuit and flow diagram is presented in this paper. There are two modes of operation of the stimulator chip-namely, stimulation mode and calibration mode. The chip also includes a digital interface used to control the stimulator parameters and calibration levels specific for each individual channel.

RESULTS

This stimulator Application Specific Integrated Circuit (ASIC) is designed and fabricated in a 0.18 μm High-Voltage CMOS technology that allows for ±20 V power supply. The full-scale stimulation current was designed to be at 1 mA per channel. The output current was shown to be constant throughout the timing cycles over a wide range of electrode load impedances. The calibration circuit was also designed to reduce the effect of CMOS process variation of the P-channel metal oxide semiconductor (PMOS) and N-channel metal oxide semiconductor (NMOS) devices that will result in charge delivery to have less than 0.13% error.

CONCLUSIONS

A 16-channel integrated biphasic neural stimulator chip with calibration is presented in this paper. The stimulator circuit design was simulated and the chip layout was completed. The chip layout was verified using design rules check (DRC) and layout versus schematic (LVS) design check using computer aided design (CAD) software. The test results we presented show constant current stimulation with charge balance error within 0.13% least-significant-bit (LSB). This LSB error was consistent throughout a variety stimulation patterns and electrode load impedances.

A CMOS Current Steering Neurostimulation Array With Integrated DAC Calibration and Charge Balancing

An 8-channel current steerable, multi-phasic neural stimulator with on-chip current DAC calibration and residue nulling for precise charge balancing is presented. Each channel consists of two sub-binary radix DACs followed by wide-swing, high output impedance current buffers providing time-multiplexed source and sink outputs for anodic and cathodic stimulation. A single integrator is shared among channels and serves to calibrate DAC coefficients and to closely match the anodic and cathodic stimulation phases. Following calibration, the differential non-linearity is within ±0.3 LSB at 8-bit resolution, and the two stimulation phases are matched within 0.3%. Individual control in digital programming of stimulation coefficients across the array allows altering the spatial profile of current stimulation for selection of stimulation targets by current steering. Combined with the self-calibration and current matching functions, the current steering capabilities integrated on-chip support use in fully implanted neural interfaces with autonomous operation for and adaptive stimulation under variations in electrode and tissue conditions. As a proof-of-concept we applied current steering stimulation through a multi-channel cuff electrode on the sciatic nerve of a rat.

An Integrated Passive Phase-Shift Keying Modulator for Biomedical Implants With Power Telemetry Over a Single Inductive Link

This paper presents a passive phase-shift keying (PPSK) modulator for uplink data transmission for biomedical implants with simultaneous power and data transmission over a single 13.56 MHz inductive link. The PPSK modulator provides a data rate up to 1.35 Mbps with a modulation index between 3% and 38% for a variation of the coupling coefficient between 0.05 and 0.26. This modulation scheme is particularly suited for biomedical implants that have high power demand and low coupling coefficients. The PPSK modulator operates in conjunction with on-off-keying downlink communication. The same inductive link is used to provide up to 100 mW of power to a multi-channel stimulator. The majority of the system on the implant side was implemented as an application specific integrated circuit (ASIC), fabricated in 0.6- [Formula: see text] high voltage CMOS technology. The theory of PPSK modulation, simulated and measured performance evaluation, and comparison with other state-of-the-art impedance modulation techniques is presented. The measured bit error rate around critical coupling at 1.35 Mbps is below 6 ×10^-8.

A Low-Power ASIC Signal Processor for a Vestibular Prosthesis

A low-power ASIC signal processor for a vestibular prosthesis (VP) is reported. Fabricated with TI 0.35 μm CMOS technology and designed to interface with implanted inertial sensors, the digitally assisted analog signal processor operates extensively in the CMOS subthreshold region. During its operation the ASIC encodes head motion signals captured by the inertial sensors as electrical pulses ultimately targeted for in-vivo stimulation of vestibular nerve fibers. To achieve this, the ASIC implements a coordinate system transformation to correct for misalignment between natural sensors and implanted inertial sensors. It also mimics the frequency response characteristics and frequency encoding mappings of angular and linear head motions observed at the peripheral sense organs, semicircular canals and otolith. Overall the design occupies an area of 6.22 mm (2) and consumes 1.24 mW when supplied with ± 1.6 V.

A CMOS Neural Interface for a Multichannel Vestibular Prosthesis

We present a high-voltage CMOS neural-interface chip for a multichannel vestibular prosthesis (MVP) that measures head motion and modulates vestibular nerve activity to restore vision- and posture-stabilizing reflexes. This application specific integrated circuit neural interface (ASIC-NI) chip was designed to work with a commercially available microcontroller, which controls the ASIC-NI via a fast parallel interface to deliver biphasic stimulation pulses with 9-bit programmable current amplitude via 16 stimulation channels. The chip was fabricated in the ONSemi C5 0.5 micron, high-voltage CMOS process and can accommodate compliance voltages up to 12 V, stimulating vestibular nerve branches using biphasic current pulses up to 1.45±0.06 mA with durations as short as 10 μs/phase. The ASIC-NI includes a dedicated digital-to-analog converter for each channel, enabling it to perform complex multipolar stimulation. The ASIC-NI replaces discrete components that cover nearly half of the 2nd generation MVP (MVP2) printed circuit board, reducing the MVP system size by 48% and power consumption by 17%. Physiological tests of the ASIC-based MVP system (MVP2A) in a rhesus monkey produced reflexive eye movement responses to prosthetic stimulation similar to those observed when using the MVP2. Sinusoidal modulation of stimulus pulse rate from 68-130 pulses per second at frequencies from 0.1 to 5 Hz elicited appropriately-directed slow phase eye velocities ranging in amplitude from 1.9-16.7 °/s for the MVP2 and 2.0-14.2 °/s for the MVP2A. The eye velocities evoked by MVP2 and MVP2A showed no significant difference ( t-test, p=0.34), suggesting that the MVP2A achieves performance at least as good as the larger MVP2.

An Embedded Deep Brain Stimulator for Biphasic Chronic Experiments in Freely Moving Rodents

This paper describes a Deep Brain Stimulation device, portable, for chronic experiments on rodents in the context of Parkinson's disease. Our goal is to equip the animal with a device that mimics the human therapeutic conditions. It implies to respect a set of properties such as bilateral current-mode and charge-balanced stimulation, as well as programmability, low power consumption and re-usability to finally reach a suitable weight for long-term experiments. After the analysis of the solutions found in the literature, the full design of the device is explained. First, the stimulation front-end circuit driven by a processor unit, then the choice of supply sources which is a critical point for the weight and life-time of our system. Our low cost system has been realized using commercial discrete components and the overall power consumption was minimized. We achieved 6 days of maximal current stimulation with the chosen battery for a weight of 13.8 g . Finally, the device was carried out in vivo on rats during a 3 weeks experiment as the used implantation technique allows battery changing. This experiment also permits to emphasize the mechanical aspects including the packaging and electrodes holding.

A vestibular prosthesis with highly-isolated parallel multichannel stimulation

This paper presents an implantable vestibular stimulation system capable of providing high flexibility independent parallel stimulation to the semicircular canals in the inner ear for restoring three-dimensional sensation of head movements. To minimize channel interaction during parallel stimulation, the system is implemented with a power isolation method for crosstalk reduction. Experimental results demonstrate that, with this method, electrodes for different stimulation channels located in close proximity ( mm) can deliver current pulses simultaneously with minimum inter-channel crosstalk. The design features a memory-based scheme that manages stimulation to the three canals in parallel. A vestibular evoked potential (VEP) recording unit is included for closed-loop adaptive stimulation control. The main components of the prototype vestibular prosthesis are three ASICs, all implemented in a 0.6- μm high-voltage CMOS technology. The measured performance was verified using vestibular electrodes in vitro.

A multichannel current stimulator chip for spatiotemporal pattern stimulation of neural tissues

We developed a prototype very-large-scale integration chip of a multichannel current stimulator for stimulating neural tissues by utilizing 0.25 μm high-voltage complementary metal-oxide-semiconductor technology. Our designed chip has 20 output channels that are driven by five current buffers arranged in parallel; each buffer controls four output channels in time-sharing mode. The amplitude of a stimulation pulse can be controlled within a range of approximately ±100 μA/phase in each output channel. The stimulus parameters, e.g., amplitude and duration, are controlled separately for each channel by digital codes stored in built-in registers. Combinations of anode and cathode electrodes to pass the current can be changed online. We integrated our stimulator chip with a multielectrode array and studied the neuronal responses to multichannel current stimulations with various temporal patterns in mouse brain slices.

Bio-inspired micro-fluidic angular-rate sensor for vestibular prostheses

This paper presents an alternative approach for angular-rate sensing based on the way that the natural vestibular semicircular canals operate, whereby the inertial mass of a fluid is used to deform a sensing structure upon rotation. The presented gyro has been fabricated in a commercially available MEMS process, which allows for microfluidic channels to be implemented in etched glass layers, which sandwich a bulk-micromachined silicon substrate, containing the sensing structures. Measured results obtained from a proof-of-concept device indicate an angular rate sensitivity of less than 1 °/s, which is similar to that of the natural vestibular system. By avoiding the use of a continually-excited vibrating mass, as is practiced in today's state-of-the-art gyroscopes, an ultra-low power consumption of 300 μW is obtained, thus making it suitable for implantation.

Advances in Microelectronics for Implantable Medical Devices

Implantable medical devices provide therapy to treat numerous health conditions as well as monitoring and diagnosis. Over the years, the development of these devices has seen remarkable progress thanks to tremendous advances in microelectronics, electrode technology, packaging and signal processing techniques. Many of today’s implantable devices use wireless technology to supply power and provide communication. There are many challenges when creating an implantable device. Issues such as reliable and fast bidirectional data communication, efficient power delivery to the implantable circuits, low noise and low power for the recording part of the system, and delivery of safe stimulation to avoid tissue and electrode damage are some of the challenges faced by the microelectronics circuit designer. This paper provides a review of advances in microelectronics over the last decade or so for implantable medical devices and systems. The focus is on neural recording and stimulation circuits suitable for fabrication in modern silicon process technologies and biotelemetry methods for power and data transfer, with particular emphasis on methods employing radio frequency inductive coupling. The paper concludes by highlighting some of the issues that will drive future research in the field.

Simultaneous neural and movement recording in large-scale immersive virtual environments

Virtual reality (VR) allows precise control and manipulation of rich, dynamic stimuli that, when coupled with on-line motion capture and neural monitoring, can provide a powerful means both of understanding brain behavioral relations in the high dimensional world and of assessing and treating a variety of neural disorders. Here we present a system that combines state-of-the-art, fully immersive, 3D, multi-modal VR with temporally aligned electroencephalographic (EEG) recordings. The VR system is dynamic and interactive across visual, auditory, and haptic interactions, providing sight, sound, touch, and force. Crucially, it does so with simultaneous EEG recordings while subjects actively move about a 20 × 20 ft² space. The overall end-to-end latency between real movement and its simulated movement in the VR is approximately 40 ms. Spatial precision of the various devices is on the order of millimeters. The temporal alignment with the neural recordings is accurate to within approximately 1 ms. This powerful combination of systems opens up a new window into brain-behavioral relations and a new means of assessment and rehabilitation of individuals with motor and other disorders.

A zero-voltage switching technique for minimizing the current-source power of implanted stimulators

The current-source power of an implanted stimulator is reduced almost to the theoretical minimum by driving the electrodes directly from the secondary port of the inductive link with a dedicated zero-voltage switching power supply. A feedback loop confined to the secondary of the inductive link adjusts the timing and conduction angle of switching to provide just the right amount of supply voltage needed for keeping the current-source voltage constant at or slightly above the compliance limit. Since drive is based on current rather than voltage, and supply-voltage update is near real-time, the quality of the current pulses is high regardless of how the electrode impedance evolves during stimulation. By scaling the switching frequency according to power demand, the technique further improves overall power consumption of the stimulator. The technique is implemented with a very simple control circuitry comprising a comparator, a Schmitt trigger and a logic gate of seven devices in addition to an on-chip switch and an off-chip capacitor. The power consumed by the proposed supply circuit itself is no larger than what the linear regulator of a conventional supply typically consumes for the same stimulation current. Still, the sum of supply and current-source power is typically between 20% and 75% of the conventional source power alone. Functionality of the proposed driver is verified experimentally on a proof-of-concept prototype built with 3.3 V devices in a 0.18 μm CMOS technology.

A field-programmable analog array development platform for vestibular prosthesis signal processing

We report on a vestibular prosthesis signal processor realized using an experimental field programmable analog array (FPAA). Completing signal processing functions in the analog domain, the processor is designed to help replace a malfunctioning inner ear sensory organ, a semicircular canal. Relying on angular head motion detected by an inertial sensor, the signal processor maps angular velocity into meaningful control signals to drive a current stimulator. To demonstrate biphasic pulse control a 1 k Ω resistive load was placed across an H-bridge circuit. When connected to a 2.4 V supply, a biphasic current of 100 μA was maintained at stimulation frequencies from 50-350 Hz, pulsewidths from 25-400 μ sec, and interphase gaps ranging from 25-250 μsec.

In situ measurement of tissue impedance using an inductive coupling interface circuit

In this work, a method of an inductive coupling impedance measurement (ICIM) is proposed for measuring the nerve impedance of a dorsal root ganglion (DRG) under PRF stimulation. ICIM provides a contactless interface for measuring the reflected impedance by an impedance analyzer with a low excitation voltage of 7 mV. The paper develops a calibration procedure involving a 50-Ω reference resistor to calibrate the reflected resistance for measuring resistance of the nerve in the test. A de-embedding technique to build the equivalent transformer circuit model for the ICIM circuit is also presented. A batteryless PRF stimulator with ICIM circuit demonstrated good accuracy for the acute measurement of DRG impedance both in situ and in vivo. Besides, an in vivo animal experiment was conducted to show that the effectiveness of pulsed radiofrequency (PRF) stimulation in relieving pain gradually declined as the impedance of the stimulated nerve increased. The experiment also revealed that the excitation voltage for measuring impedance below 25 mV can prevent the excitation of a nonlinear response of DRG.

A dual-mode highly efficient class-E stimulator controlled by a low-Q class-E power amplifier through duty cycle

This paper presents the design flow of two high-efficiency class-E amplifiers for the implantable electrical stimulation system. The implantable stimulator is a high-Q class-E driver that delivers a sine-wave pulsed radiofrequency (PRF) stimulation, which was verified to have a superior efficacy in pain relief to a square wave. The proposed duty-cycle-controlled class-E PRF driver designed with a high-Q factor has two operational modes that are able to achieve 100% DC-AC conversion, and involves only one switched series inductor and an unchanged parallel capacitor. The measured output amplitude under low-voltage (LV) mode using a 22% duty cycle was 0.98 V with 91% efficiency, and under high-voltage (HV) mode using a 47% duty cycle was 2.95 V with 92% efficiency. These modes were inductively controlled by a duty-cycle detector, which can detect the duty-cycle modulated signal generated from the external complementary low-Q class-E power amplifier (PA). The design methodology of the low-Q inductive interface for a non-50% duty cycle is presented. The experimental results exhibits that the 1.5-V PA that consumes DC power of 14.21 mW was able to deliver a 2.9-V sine wave to a 500 Ω load. The optimal 60% drain efficiency of the system from the PA to the load was obtained at a 10-mm coupling distance.

Development of a multichannel vestibular prosthesis prototype by modification of a commercially available cochlear implant

No adequate treatment exists for individuals who remain disabled by bilateral loss of vestibular (inner ear inertial) sensation despite rehabilitation. We have restored vestibular reflexes using lab-built multichannel vestibular prostheses (MVPs) in animals, but translation to clinical practice may be best accomplished by modification of a commercially available cochlear implant (CI). In this interim report, we describe preliminary efforts toward that goal. We developed software and circuitry to sense head rotation and drive a CI's implanted stimulator (IS) to deliver up to 1 K pulses/s via nine electrodes implanted near vestibular nerve branches. Studies in two rhesus monkeys using the modified CI revealed in vivo performance similar to our existing dedicated MVPs. A key focus of our study was the head-worn unit (HWU), which magnetically couples across the scalp to the IS. The HWU must remain securely fixed to the skull to faithfully sense head motion and maintain continuous stimulation. We measured normal and shear force thresholds at which HWU-IS decoupling occurred as a function of scalp thickness and calculated pressure exerted on the scalp. The HWU remained attached for human scalp thicknesses from 3-7.8 mm for forces experienced during routine daily activities, while pressure on the scalp remained below capillary perfusion pressure.

Replacing semicircular canal function with a vestibular implant

PURPOSE OF REVIEW

To summarize the recent progress in the development of vestibular implants. The review is timely because of the recent advances in the field and because MED-EL has recently announced that they are developing a vestibular implant for clinical applications.

RECENT FINDINGS

The handicap experienced by patients suffering from bilateral vestibulopathy has a strong negative impact on physical and social functioning that appears to justify a surgical intervention. Two different surgical approaches to insert electrodes to stimulate ampullary neurons have been shown to be viable. The three-dimensional vestibulo-ocular reflex in rhesus monkeys produced with a three-dimensional vestibular implant showed gains that were relatively normal during acute stimulation. Rotation cues provided by an implant interact with otolith cues in a qualitatively normal manner. The brain appears to adapt plastically to the cues provided via artificial electrical stimulation.

SUMMARY

Research to date includes just a few human studies, but available data from both humans and animals support the technological and physiological feasibility of vestibular implants. Although vestibular implant users should not expect normal vestibular function - any more than cochlear implant users should expect normal hearing - data suggest that significant functional improvements are possible.

A tripolar current-steering stimulator ASIC for field shaping in deep brain stimulation

A significant problem with clinical deep brain stimulation (DBS) is the high variability of its efficacy and the frequency of side effects, related to the spreading of current beyond the anatomical target area. This is the result of the lack of control that current DBS systems offer on the shaping of the electric potential distribution around the electrode. This paper presents a stimulator ASIC with a tripolar current-steering output stage, aiming at achieving more selectivity and field shaping than current DBS systems. The ASIC was fabricated in a 0.35-μ m CMOS technology occupying a core area of 0.71 mm(2). It consists of three current sourcing/sinking channels. It is capable of generating square and exponential-decay biphasic current pulses with five different time constants up to 28 ms and delivering up to 1.85 mA of cathodic current, in steps of 4 μA, from a 12 V power supply. Field shaping was validated by mapping the potential distribution when injecting current pulses through a multicontact DBS electrode in saline.